The present invention relates to the field of surface mounted chip carriers and more particularly to tools for soldering such chip carriers to a substrate or de-soldering such chip carriers from a substrate to which they have been soldered.
Small (0.500 inch by 0.500 inch) surface mounted chip carriers may have as many as 40 contact pads thereon (10 per side) which must be soldered to mating contact pads on a printed circuit substrate. The printed circuit substrate may take any appropriate form such as a ceramic printed circuit substrate, a printed circuit board, a porcelain coated metal printed circuit board and so forth.
There are well developed techniques for simultaneously soldering a plurality of surface mounted chip carriers to a printed circuit substrate. Subsequent to such mass soldering of chip carriers to a printed circuit substrate the need sometimes arises to non-destructively remove one or more of the chip carriers. There are problems with present day techniques for such de-soldering of chip carriers from a printed circuit substrate.
When a chip carrier must be removed from a printed circuit substrate, the solder between all of its contact pads and the printed circuit substrate must be made molten at the same time. This requires a substantial amount of heat distributed around the periphery of the chip carrier. Application of too much heat in this process can damage the semiconductor chip mounted inside the chip carrier.
Conventional soldering equipment such as soldering irons is incapable of rendering all of the solder connections molten at the same time. One technique which is used for de-soldering chip carriers is to direct a jet of hot gas at the chip carrier to melt the solder. U.S. Pat. No. 4,295,596 to Doten et al. discloses a tool which includes a plurality of individual gas jets each directed at a different individual contact pad for de-soldering chip carriers. This tool has the disadvantage of being complicated and being limited by its gas jet configuration to a specific chip carrier package size and contact pad configuration.
There is a need for a simple tool for removing surface mounted components from printed circuit substrates without, during normal operation, damaging the components so mounted.